Currently, the mainstream method of displaying a color image with a liquid crystal display apparatus is by using a backlight apparatus to illuminate a transparent type liquid crystal display panel having a color filter from behind. Although CCFL (Cold Cathode Fluorescent Lamp) using fluorescent tubes were used for most backlights, their use of mercury is being controlled for preventing environmental problems. Light emitting diodes (LED) are being used as light sources as alternatives of the CCFL using mercury (See, for example, Patent Document 1).
The backlight apparatus for a liquid crystal panel is largely categorized into a direct type and an edge type. The direct type is a type in which a light source is positioned directly below a back side of a liquid crystal panel. The edge type is a type in which a light guidance plate is positioned directly below a backside of a liquid crystal panel and a light source is positioned at a side part of the light guidance plate. The edge type is already mainly used for comparatively small liquid crystal panels such as displays of mobile phones and laptop computers.
Further, as for a backlight apparatus using a light emitting diode as its light source, there is a type using a white light emitting diode and a type obtaining a white light by mixing colors of light emitting diodes of three primary colors of red, green, and blue.
However, the same as the backlight apparatus using CCFL, the backlight apparatuses using the light emitting diodes are constantly lit with a high luminance during use of the liquid crystal display apparatus and there is a demand to reduce power consumption. Therefore, in Patent Document 2, reduction of power consumption is proposed by dividing backlight into plural sub-units and adjusting luminance of each sub-unit.
Typically, because light emitting diodes have largely varying luminance and chromaticity, random use of light emitting diodes will cause uneven chromaticity and adversely affect image quality. Therefore, it is necessary to sort light emitting diodes. As a method of using such variable light emitting diodes, there is, for example, Patent Document 3.
Patent Document 1: Japanese Laid-Open Patent Publication No. 7-191311
Patent Document 2: Japanese Laid-Open Patent Publication No. 2004-191490
Patent Document 3: Japanese Laid-Open Patent Publication No. 2006-133708